The present invention relates to a stirrer stand for a submersible motor stirrer.
Submersible motor stirrers are stirrers which are used together with the drive under water. They are usually employed in water treatment plants, in wastewater purification and wastewater treatment for different process-engineering stirring functions within various fields of use. The stirrer stand serves to position the stirrer in such a way in a liquid-filled basin, a corresponding plant or the like that a defined distance is maintained between the bottom of the basin and the tip of the stirring member, on the one hand, and the tip of the stirring member and the liquid level, on the other hand, which distance assures the best possible working of the stirrer.
The function of the stirrer is basically to provide good flow guidance in the respective basin or the plant in order to achieve the respective process-engineering function, for example good intermixing of several phases. The stirrer stand must absorb all forces and moments which, on the one hand, arise from the work of the stirrer itself and, on the other hand, stem from the liquid in motion in the basin or in the flow channel and from the further phases, such as gases and liquids, which may be contained therein. The absorbed forces and moments must be relayed to the subsurface, for example the bottom of the basin, or diverted into this.
Within the scope of the invention, the term stirrer stand is used. In the same way, the stirrer stand which is present here can also be used, however, as a stand for a turbine. While the stirrer has the function of generating flows, of distributing temperature and gas content, as well as microbes and further additives, e.g. for wastewater purification, and is thus used for water treatment or for other process-engineering processes, the function of a turbine is to absorb energy from a flowing stream in which it is immersed and to generate electric current.
Stirrer stands for submersible motor stirrers or turbines are already known in different embodiments.
For instance, stirrer stands constructed of steel and consisting of welded-together profiles are known. These steel constructions are usually connected to the guide member, configured as a guide tube, for the submersible motor stirrer. This enables the submersible motor stirrer, during assembly, to be transferred via the guide member into its assembly position and to be held there by the guide member, the absorbed forces being transferred via the guide member to the whole of the steel construction.
DE 39 00 630 discloses a submersible motor stirrer in which the guide tube is fixedly connected only to the bottom of the basin and in which two supports are provided for absorbing the reaction forces of the stirrer comprising a motor and a propeller, which supports are fastened, on the one hand, beneath the stirrer to the guide tube and, on the other hand, to the bottom of the basin.
In the various basins in which the submersible motor stirrers are disposed, irregular flows occur, so that the stirring member of the submersible motor stirrer is impinged upon or subjected to irregular flows. In addition, the turbulence generated by the flow around the base frame is problematic. The irregular oncoming flows lead to vibrations within the base frame, so that both the submersible motor stirrer and the base frame are subjected to above-average load.
In order to produce a mounting for a submersible motor stirrer which is as low in vibrations as possible, EP 980,704 proposes to produce the guide member, which protrudes vertically beyond the stirrer stand and which is there configured as a guide tube, from a first material, for example steel, and to produce the stirrer stand itself from a second material, for example concrete, which has different vibration characteristics than the first material. In the installed position, the submersible motor stirrer is still connected to the guide member consisting of the first material. While the stirrer stand made of concrete is now itself almost perfectly rigid, the more elastic guide member, which, even in the installed position of the submersible motor stirrer, is connected thereto, simultaneously absorbs a part of the generated forces and moments.
The previously known stirrer stands have various drawbacks, however. For instance, stirrer stands which are made entirely of high-quality steel, are very costly and, because of the lack of internal damping, are also very prone to vibration. The use of several materials, which is known from EP 980,704, additionally calls for assembly and jointing processes. The transmission of torques and forces to the guide tube, which transmission is provided according to this solution, requires the guide tube to have a solid design. This, in turn, leads to vibrations in the event of fluctuating loads.